Here she comes, frantic and dressed for work, with coughing and sniffling tot in tow. And kindergarten teacher Mariessa Doherty is there to greet her.

“She’ll say, ‘Well, we’ve had a rough morning, but I really need to get to work,’” says Doherty.As a mother of three, Maya Bunik has also been there, but she lets the school know if one of her kids is under the weather. “I’ll tell them we might be coming down with something, but I’m not sure and I need them to understand we’re trying to make it through today,” she says.

Of course, Bunik has an advantage when trying to decide whether her kids are too sick for school. She’s medical director of the Child Health Clinic at The Children’s Hospital in Denver. For other parents – especially those juggling the demands of work and family, and pressure from schools to boost both attendance and test scores – it isn’t so easy.

After six years in teaching, Doherty has seen plenty of kids in her classroom whose parents should have kept them home. “You can just see them struggling,” she says. “They don’t get anything out of the school day, and they end up getting all the other kids sick.”

Always keep your child home if …

He has a fever. This means a temperature at or above 101 degrees Fahrenheit. With fever at this level, even if your child doesn’t have additional symptoms, he or she is “brewing an infection,” says pediatrician Vicki Iannotti, M.D.

She has vomited two or more times. A single episode of vomiting could be brought on by any number of things – nerves or too much bouncing around – so wait until it happens twice before you worry. “The problem with vomiting is, it’s such a dramatic event,” says Bunik.

He has diarrhea. Watery or loose stools mean you’re likely dealing with a virus, meaning you should keep your child at home and make sure she drinks lots of water. But if your child has diarrhea with blood or mucus in it, he needs to visit the doctor, as this could be a bacterial infection.

She is coughing or having any sort of breathing trouble. Coughing spreads infection. And a cough that keeps your child up at night means she’ll be too tired to learn the next day.

He has a rash that is spreading. Check with your doctor to determine whether the rash is contagious before sending your child to school.

She is lethargic. Iannotti stresses that “lethargic” is beyond just acting tired. “Most parents use lethargy in a looser sense than we do,” she says. However, a child who is truly difficult to wake, or whose behavior suddenly makes a dramatic shift, needs to see a doctor.

Confounding Fever

Of course, illness isn’t always this simple. For instance, if your child feels “warm,” but doesn’t quite hit the 101-degree mark, you’ll have to look for additional clues. Is he grumpy or crying a lot? Is he acting like he doesn’t feel well?

“It’s not so much the height of the fever. It’s how the kid looks when he’s having the fever,” says Bunik.

School nurse Susan Marley, R.N., a board member of the National Association of School Nurses, sees plenty of kids who were given an a.m. dose of Motrin and sent to school. “It wears off around 1 p.m.,” she says. So the child spends the morning exposing classmates to infection, and has to be picked up by early afternoon.

What kids with fever really need is time at home to rest – until they’ve been fever-free for at least 24 hours.

Nonstop Sniffles

Everyone, really, would prefer that sick kids stay home. But, because they catch colds so frequently, kids kept home for every sniffle would spend more days out of school than in. And sometimes it’s OK to send a child with a cold to school.

“Evaluate that runny nose in light of how the child is doing in general,” Iannotti advises. As long as your child doesn’t have high fever, vomiting, diarrhea or cough, she probably doesn’t need to stay home.

Pediatrician Michael Bryant, M.D., points out that kids’ poor hand-washing habits make school an easy place to get sick.

“It really provides sort of a cesspool for trading germs,” he says. Yet Bryant doesn’t tell patients with minor colds that they have to stay home.

And, while looking out for the other kids in the class is a nice idea, Bunik says it’s almost impossible to pinpoint which days your child might be contagious. A more effective strategy is to teach your child about good hand-washing, using disposable tissues to wipe their nose, and coughing into their sleeve.

Middle-Ear Madness

Almost as common as colds, and sometimes coming right on their heels, middle-ear infections are another bane of childhood. As long as the infection isn’t happening along with a cold, if your child feels fine, it’s fine to go to school, according to Iannotti.

But not all kids with ear infections feel fine. “The issue with ear infections is that they can be very painful,” says Bryant. “However, some kids can have a raging ear infection with almost no discomfort at all.”

Because kids in pain just can’t concentrate, it’s better to keep them home until the infection and pain subside.

Tummy Trouble

A child with a stomachache who also has fever, diarrhea or vomiting should always be kept home from school, and often even needs to see a doctor. But what about those other stomachaches – the ones that seem to come out of nowhere?

Bunik suggests that you send your child to lie down and rest, because a child who isn’t truly ill won’t stay down for long. Meanwhile, ask a few key questions:

What has your child eaten lately? Food could be the cause.

When was the last time your child went to the bathroom? Bunik places constipation among the top five causes of children’s stomach pain. Was their last stool “long like a log or round like a ball”? Was it tough to get out? If so, see your doctor.

Is your child worried about something going on at school? “There are lots of kids that get stomachaches because they don’t want to go to school,” says Marley. The cause could be anything from a big test to trouble with the class bully, so visit the school to find out what’s up.

“The worst thing they can do is keep the child home,” she says, because this sends the message that school is a bad place.

Whatever the cause, if the stomachache lasts two days or more, the child needs to be seen by a doctor.

After the Antibiotics

Many contagious illnesses require a course of antibiotics. In general, treatment needs to be under way for a day or two before your child can return to school.

“Once they have gotten 24 to 48 hours of therapy, they not only feel better, they are likely minimally contagious,” says Bryant. But each illness has specific guidelines regarding when it’s OK to return to school:

Strep throat – 24 hours on antibiotics

Conjunctivitis – once antibiotics have been started

Pertussis – at least 5 days of treatment

Impetigo – 24 hours of antibiotics

To help prevent one of the most common side-effects of antibiotic treatment, diarrhea, Iannotti advises giving your child either yogurt or a supplement with Lactobacillus acidophilus. “It helps keep the intestinal flora balanced,” she explains.

Keeping in Touch

If your child is on antibiotics and returning to school, Marley suggests letting the school know so staff can be on the lookout for side-effects, such as nausea, diarrhea and fatigue. “The more information we have from the parent, the easier it is for the nurse to give the best care,” she says.

When in doubt about a possible illness, contact the school to find out whether any illness has been going around. Experts generally advise erring on the side of caution.

Iannotti also reminds parents that illness doesn’t always come with dramatic symptoms, so contact your doctor if your child’s sleep, appetite, activity level, mood or coloring seems off for more than a day. “Sometimes the more serious stuff is less dramatic,” she says. “Pay attention to the subtle changes.”